1. Field of the Invention
The present invention relates to a data recording apparatus and method, and a data playback apparatus and method, for digital data such as video and audio information in a movie or the like.
2. Description of the Related Art
The digital apparatuses for recording and/or playing back digital data to and/or from a recording medium include digital VTRs (video tape recorder).
Supplied with digital data having the MPEG (Moving Picture coding Experts Group) format or digital data having the so-called DV (digital video) format, the digital VTR records it in a recording tape as a recording medium, and also plays back digital data from the tape and provides it to outside. The digital VTR can record and/or play back digital data with higher tone quality and image quality, and edit the data more easily than the ordinary VTR which records and/or plays back analog data to and/or from a recording medium.
For permitting to write digital data supplied from outside to a recording tape, the above-mentioned digital VTR processes the digital data in a predetermined manner such as modulation and the like for recording to the tape at a predetermined data rate. Also, the digital VTR plays back digital data from the recording tape at a predetermined data rate, processes it in a predetermined manner such as demodulation and the like for output to outside.
However, since the digital VTR records and plays back data at a constant tape feed speed, it can only record data for a fixed length of time depending upon the tape feed speed, not upon a data rate of an actual input stream. For example, a video tape with a recording tune of one hour is a one having a recording time depending upon a tape feed speed. Assume here that an input stream of which the data rate is 10 Mbps or 5 Mbps is recorded by a digital VTR designed to record and play back data to and from a recording medium at a data rate of 14.1 Mbps for example. In this case, the amount of digital data which can be recorded to the recording medium is the product of the data rate (14.1 Mbps) of the digital VTR in recording to the recording medium and the length of tape feeding time (one hour or 3,600 seconds in this case), that is, of 14.1 Mbps by 3,600 seconds. However, if the amount of digital data, which can only be recorded to the recording medium is a product of the data rate (10 Mbps or 5 Mbps) of the input stream and the length of tape feeding time (3,600 seconds in this case), namely, a time length of 10 Mbps or 5 Mbps by 3,600 seconds. In this case, the digital VTR has to record dummy data to the greatest part of the recording medium or tape. Thus, the tape cannot effectively be used for data recording.
It is therefore an object of the present invention to overcome the above-mentioned drawbacks of the prior art by providing a data recording apparatus and method, and a data playback apparatus and method, which can effectively use the recording capacity of a recording tape by intermittent recording and playback of data to and from the recording tape.
According to the present invention, there is provided a data recorder to record external input data to a recording medium at a first data rate DL1, the apparatus including:
a memory means for storing data supplied at a second data rate DL2;
a data rate changing means for intermittently reading the data stored in the memory means and providing the data as an output; and
a controlling means for driving the recording medium intermittently according to the data provided from the data rate changing means;
the data rate changing means reading the data intermittently from the memory means so that the first data rate DL1 is a momentary data rate at which the data rate changing means reads the data read from the memory means and provides it as the output while the second data rate DL2 is a mean data rate at which the data rate changing means reads the data read from the memory means and provides it as the output.
The above data recorder records data intermittently by the memory means for storing the data at the mean data rate, data rate changing means for changing the mean data rate to the momentary data rate, and the controlling means for driving the recording medium intermittently according to the change of the data rate. Thus, for data recording, the data recorder can make the most of the recording capacity of the recording medium.
According to the present invention, there is also provided a method of recording an external input data to a recording medium at a first data rate DL1, the method including steps of:
storing into a memory means data supplied at a second data rate DL2;
reading data intermittently from the memory means and providing it as an output so that the first data rate DL1 is a momentary data rate of the data read from the memory means and provided as the output while the second data rate DL2 is a mean data rate of the data read from the means and provided as the output; and
driving the recording medium intermittently according to the output data.
In the above recording method, the data supplied at the second data rate DL2 is stored into the memory means, and then the data is read from the memory means by the data rate changing means at the first data rate DL1, and the recording medium is driven intermittently by the controlling means according to the change of the data rate. Thus, for data recording, the data recording method permits to make the most of the recording capacity of the recording medium.
According to the present invention, there is also provided a data reproducer to read data from a recording medium at a first data rate DL1, the apparatus including:
a controlling means for driving the recording medium intermittently for data reading;
a memory means for storing data read from the recording medium; and
a data rate changing means for writing into the memory means the data read from the recording medium and providing it as an output at a second data rate DL2;
the controlling means driving the recording medium intermittently so that the first data rate DL1 is a momentary data rate of the data read from the recording medium and provided to the data rate changing means while the second data rate DL2 is a mean data rate of the data read from the recording medium and provided to the data rate changing means.
The above data reproducer reads data from the recording medium intermittently and changes the data rate by the controlling means for driving the recording medium intermittently, memory means for storing the data at the first data rate DL1, and the data rate changing means for changing the first data rate DL1 to the second data rate DL2. Thus, for data reproduction, the data reproducer can play back data from the recording medium making the most of the recording capacity of the latter.
Therefore, even when the data reproducer is used with any external device which provides data at a data rate different from the reading data rate of the data reproducer, the data rate changing means changes the data rate to an appropriate one to enable the data output to the external device.
According to the present invention, there is also provided a method of playing back data from a recording medium at a first data rate DL1, the method includes steps of:
reading data from the recording medium driven intermittently under the control of a controlling means;
storing the data read from the recording medium into a memory means; and
reading the data stored in the memory means and providing it as an output at a second data rate DL2;
the controlling means driving the recording medium intermittently for data playback so that the first data rate DL1 is a momentary data rate of the data read from the recording medium while the second data rate DL2 is a mean data rate of the data read from the recording medium.
In the above recording method, data is read from the recording medium by driving the recording medium intermittently under the control of the controlling means, the data is stored into the memory means at the first data rate DL1, and the first data rate DL1 is changed to the second data rate DL2 by the data rate changer. Thus, for data reproduction, this method permits to read data from the recording medium making the most of the recording capacity of the latter.